New undersea and terrestrial lightwave systems are being considered that will use erbium-doped fiber amplifiers rather than currently used opticalelectronic regenerators to boost the optical signal. In a multi-channel optical transmission system, such as wavelength division multiplexed systems, where two or more signals of different frequencies are used to transmit information, it is imperative that each of the channels have equal transfer functions (gain as a function of wavelength) In long haul transmission systems, if the gain of one channel at an amplifier is different from that of another channel, even by as small as 0.1 dB, through each of the amplifiers, serious problems can result. Let us assume that in each amplifier of a long haul transmission line, channel A of wavelength .lambda..sub.1 experiences a gain which is 0.1 dB greater than channel B of wavelength .lambda..sub.2, and that the transmission line contains 100 amplifiers from end-to-end. Then, after passing through the 100 amplifiers, signal .lambda..sub.1 of channel A can be as much as 10 dB greater than signal .lambda..sub.2 of channel B. This difference of signal level between the two channels can result in an optical transmission system which, at best, may be marginal in performance. For example, if after passing through 100 amplifiers channel A is at a level which provides a good signal to noise ratio, the channel B which experienced less gain, may be at a signal level which has a very low signal to noise ration and may be too low to be useful. Additionally, each amplifier can provide only a finite amount of power to the signals being amplified. In practice, it has been observed that while the power of the amplifier is available to both channels, frequently it is not divided equally between the two channels. Often, the larger of the two signals will capture a proportionately larger portion of the available power and leave a disproportionate smaller share of the available power for the weaker signal. Thus, the stronger signal gets progressively stronger, relative to the weaker signal, as the two signals advance through the various amplifiers of a long haul transmission line. Clearly, a need exists for amplifier gain equalization in an optical fiber amplifier.